Her father, Ryan Allen, dipped his pinky in cream cheese icing and stuck it in her mouth. Her tongue worked the sugar. Her coo turned to a trill.

This birthday party was never supposed to happen.

Riley Allen was born Dec. 4, 2011, with a genetic defect so severe doctors had advised her mother to terminate the pregnancy. But Adeline Sullivan decided to go forward. Riley weighed 2 pounds at birth, and doctors gave her a 50 percent chance of living past the first weeks. The odds of surviving a year, they said, were less than 1 in 10.

But weeks stretched into months, and Addie and Ryan learned to operate oxygen tanks, feeding tubes and suction machines. They doled out medications five times a day, scheduled regular appointments with eight doctors and opened their door for three therapists a week.

With so much responsibility and no jobs, Addie, 21, and Ryan, 27, sometimes question their relationship with each other. But never their decision to have Riley, which was chronicled in the Tampa Bay Times in May.

"I don't know what I'd do without her," Addie said Sunday.

Riley is still only 15 pounds, but her parents no longer worry that she will die in her sleep.

On Sunday, wearing a pink dress with black lace, Riley cried and smiled and laughed. She went from arm to arm between friends and family, before her mother placed her in a high chair and sat the cake in front of her.

• • •

Riley was a month old when she was released from All Children's Hospital to be cared for at home by Suncoast Hospice. When she was nearly 6 months old, a Hospice nurse and social worker handed her parents a certificate. Riley had graduated.

In June, Riley started speech therapy, which was really to help her learn to eat. Riley had a feeding tube inserted down her nose after birth and later a tube in her abdomen. Now she is fed five bags of formula each day through the tube.

Often, kids with Trisomy 18 never eat solid food. Riley has been trying. She likes rice cereal and pureed vegetables and fruits, especially mangoes. She consumes about half a baby spoon full at a time.

In July, Carolyn Gibson, a physical therapist assistant, started working with Riley to help her learn to roll over and to sit leaning on her arms — skills that a 2- or 3-month-old child would have mastered. No one knows yet about her cognitive level.

As she does with her other patients, Gibson shows Addie and Ryan how to build their daughter's strength.

"I know who does their homework and who doesn't," Gibson said. "These two do."

Gibson said she sees the cracks that threaten to break the family apart, but also the bond they share with their child.

"She's the glue," Gibson said of Riley. "She's the middle of the Oreo."

• • •

Addie has been bugging Ryan to marry her. Ryan says he isn't ready for marriage. "Maybe when I'm 40," he said. Addie wants Riley dedicated in her grandmother's church. But the pastor won't do it for unmarried parents.

Ryan's mother, Lissa Cunningham, lives down the street in the mobile home park and sometimes babysits. Still, the parents rarely get free time together. When they do arrange for a baby-sitter, there's the problem of little money to do anything.

Ryan has worked a few short-term jobs during the past seven months. Last month he was fired from an auto body repair shop when he had to take time off to take Riley to a doctor's appointment. Addie doesn't have a driver's license or a job.

Medicaid covers Riley's bills. Sometimes a list of charges comes in the mail. After seeing one for more than $400,000, her parents stopped opening the envelopes. Medicaid pays $475 a week for Riley's therapy.

The family lives on Riley's Social Security disability check and by renting out a room in the mobile home that Addie's grandmother owns. They put together TVs and computers that they sell. When they have a few extra dollars, they go out for breakfast at the Old Cape Cod Kitchen, a short walk from their home.

They held the party here. There were gifts: Riley's first baby doll, lots of clothes and a toy laptop computer. Then Addie planted Riley's tiny hands into the soft cake.

After Addie washed off Riley, she and Ryan took down the decorations and moved tables and talked. Riley, hooked to her last feeding bag of the day, sat in her car seat and fell asleep.

Elisabeth Parker can be reached at eparker@tampabay.com or (813) 226-3431.